Which Massachusetts marshes can survive in rising seas?

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In some coastal areas, saltwater marshes could migrate inland as sea levels rise, giving them a unique ability to adapt to a changing environment.

In some coastal areas, saltwater marshes could migrate inland as sea levels rise, giving them a unique ability to adapt to a changing environment.

Funded by the U.S. Fish and Wildlife Service, The Nature Conservancy recently analyzed coastal topography from Maine to Virginia to identify “coastal strongholds,” or marshes with conditions that make them the most resilient to sea-level rise. The largest such “stronghold” in Massachusetts is the Great Marsh, which spans several communities north of Gloucester. The research identified several other resilient marshes, including the North River estuary in Marshfield and Scituate, the Great Marshes in Barnstable and Allens Pond Wildlife Sanctuary in Dartmouth.

The strongholds, lead study author Mark Anderson explained, are not immune to the effects of rising oceans, but are best situated to migrate into adjacent areas inland. But many marshes near cliffs or hills, he said, would likely be wiped out by rising sea levels because the topography would prevent them from moving inland.

While coastal marshes are ecologically important areas that provide habitats for rare species and rival rainforests in their ability to trap carbon, they also play a vital role in protecting nearby developments. During hurricanes and intense storms, marshes are able to absorb much of the accompanying storm surge, providing shielding nearby communities from floodwaters, said Anderson, a conservation scientist with The Nature Conservancy.

“The problem is that once these marshes are fully inundated under sea level rise, those properties go away,” he said. “We want to make sure we still have them there.”

Zoom in to explore the map. Click the menu button in the upper left corner of the map, then select "Resilience score (6 foot scenario)." The Nature Conservancy analyzed coastal marshes to identify which are best suited to survive sea level rise. Green areas of the map are best able to migrate inland to survive. The brown areas were identified as the least resilient marshes.

Identifying “coastal stronghold” marshes can help land managers prioritize their conservation efforts, said David Eisenhauer, a spokesman for the U.S. Fish and Wildlife Service.

“To ensure that coastal communities continue to benefit from storm surge protection provided by healthy tidal marsh systems in the face of more intense storms, we need to make sure we leave these systems room to grow as the environment changes,” he said. “Likewise, in order to meet our responsibilities for protecting fish and wildlife, managers of coastal refuges are realizing they need to think not only about where habitats are now, but where they are going to be in the future.”

The data, he said, can help land managers put conservation resources into the marshes that have the best chances of surviving.

“This tool gives land managers working at any scale the ability to look for coastal areas where healthy tidal marsh systems can be sustained over time if we take the right action at those sites today,” Eisenhauer said. “For example, states and conservation partners can use the information to target investments and conserve priority habitats for species like salt marsh sparrow, black rail and American black ducks.”

Even in the identified coastal stronghold marshes, human development such as roads, seawalls and other structures could prevent the ecosystem from migrating and re-establishing itself inland, Anderson said.

He discussed The Nature Conservancy’s modeling under a 6-foot sea level rise.

“One of the big take-home messages is even if every marsh migrated exactly the way we hoped it would, we’d only have about 66 percent of what we have right now,” he said. “But if none migrated, we’d be down to 17 percent.”

One of his goals is to help people understand and embrace the concept of marshland migration.

“There is still going to be some loss of marshland, but if the marshes could migrate, we could retain those coastal marshes and all of the good services they provide for people and wildlife.”

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